This invention relates to a catalytic technique for upgrading olefin streams rich in dienes to heavier hydrocarbons rich in aromatics. In particular, it provides a catalytic process for oligomerizing a feedstock containing monoalkenes and dienes to produce C.sub.5.sup.+ hydrocarbons rich in C.sub.6 -C.sub.10 aromatics, such as benzene, toluene, xylenes, tri- and tetramethyl benzenes, along with fuels and other useful products. Diene-containing liquids, such as thermal cracking byproduct, are useful feedstocks herein.
Developments in zeolite catalysts and hydrocarbon conversion processes have created interest in utilizing olefinic feedstocks for producing C.sub.5.sup.+ gasoline, diesel fuel, etc. In addition to basic chemical reactions promoted by ZSM-5 type zeolite catalysts, a number of discoveries have contributed to the development of new industrial processes. These are safe, environmentally acceptable processes for utilizing feedstocks that contain olefins. Conversion of C.sub.2 -C.sub.4 alkenes and alkanes to produce aromatics-rich liquid hydrocarbon products were found by Cattanach (U.S. Pat. No. 3,760,024) and Yan et al (U.S. Pat. No. 3,845,150) to be effective processes using the ZSM-5 type zeolite catalysts. In U.S. Pat. Nos. 3,960,978 and 4,021,502, Plank, Rosinski and Givens disclose conversion of C.sub.2 -C.sub.5 olefins, alone or in admixture with paraffinic components, into higher hydrocarbons over crystalline zeolites having controlled acidity. Garwood et al. have also contributed to the understanding of catalytic olefin upgrading techniques and improved processes as in U.S. Pat. Nos. 4,150,062, 4,211,640 and 4,227,992. The above-identified disclosures are incorporated herein by reference.
Conversion of olefins, especially alpha-monoalkenes such as propene and butenes, over HZSM-5 is effective at moderately elevated temperatures and pressures. The conversion products are sought as liquid fuels, especially the C.sub.5.sup.+ aliphatic and aromatic hydrocarbons. Product distribution for liquid hydrocarbons can be varied by controlling process conditions, such as temperature, pressure and space velocity. Aromatic gasoline (C.sub.5 -C.sub.10) is readily formed at elevated temperature (e.g., about 425.degree. to 650.degree. C.) and moderate pressure from ambient to about 5500 kPa, preferably about 200 to 2900 kPa. Olefinic gasoline can also be produced and may be recovered as a product or fed to a low severity, high pressure reactor system for further conversion to heavier distillate range products or otherwise utilized. Operating details for typical "MOGD" oligomerization units are disclosed in U.S. Pat. Nos. 4,456,779; 4,497,968 (Owen et al.) and 4,433,185 (Tabak), incorporated herein by reference.
Many feedstocks of commercial interest, such as thermal cracking byproduct, etc., contain both mono-olefins and diolefins (e.g. C.sub.2 -C.sub.6 mono-alkenes and C.sub.4.sup.+ dienes) along with light alkanes and aromatics. Gaseous and liquid streams containing dienes are typically produced in thermal cracking operations. One common example is pyrolysis gasoline which is produced as ethane (ethylene) cracking byproduct. Such diene-containing streams are often difficult to process due to poor thermal stability and the tendency of dienes to form coke and gum deposits. This complicates preheating of such streams into the high temperatures required of most catalytic upgrading processes. Prior attempts to upgrade such materials have pretreated the feedstock to hydrogenate the dienes selectively, as in U.S. Pat. No. 4,052,477 (Ireland et al). The present invention is concerned with providing a safe and low cost alternative to catalytically converting olefinic streams to high value C.sub.5.sup.+ products, rich in aromatic hydrocarbons, including monocyclic benzenoids having 6 to 8 carbon atoms. The inventive process may be employed in converting paraffinic feedstocks containing diene components under aromatization reaction conditions.